High voltage bushing for horizontal mounting with sheds protecting a substantial portion of the creep distance along the surface of the bushing from atmospheric fallout



Oct. 25, 1966 c. F. SONNENBERG ETAL 3,281,525

HIGH VOLTAGE BUSHING FOR HORIZONTAL MOUNTING WITH SHEDS PROTECTING A SUBSTANTIAL PORTION OF THE CREEP DISTANCE ALONG THE SURFACE OF THE BUSHING FROM ATMOSPHERIC FALLOUT Filed Feb. 7, 1964 Fig.3.

WITNESSES lNVENTORS Charles E Sonnenberg JZMM/ and mes H. Frokes United States Patent 3,281,525 HIGH VOLTAGE BUSHING FOR HORIZONTAL MOUNTING WITH SHEDS PROTECTING A SUBSTANTIAL PORTION OF THE CREEP DISTANCE ALONG THE SURFACE OF THE BUSHING FROM ATMOSPHERIC FALLOUT Charles F. Sonnenberg and James H. Frakes, Penn Hills, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Feb. 7, 1964, Ser. No. 343,369 5 Claims. (Cl. 174211) This invention relates to high voltage bushings, and more particularly to high voltage bushings suitable for mounting in positions other than vertical including horizontal positions, in areas of atmospheric contamination and areas of recurring moisture condensation.

In the past, trouble has been encountered with high voltage bushings mounted in a horizontal position, because over a period of time a deposit of contaminant material develops on the surface of a bushing. This contaminant or atmospheric fall out may be due to the presence of dust, smoke, pollen or other dry vegetable matter etc. in the atmosphere. When this deposit of contaminant is wet slightly, such as by fog or condensation, the resistance of the creepage path along the surface of the bushing may become so small that fiashover occurs. This fiashover may result from an ionized path, the formation of which is made relatively easy by the presence of impurities in the Water or moisture on the surface.

Our invention provides a high voltage bushing composed of, for example, porcelain, suitable for mounting in a horizontal position, and in which a minimum of surface is exposed to direct vertical fallout; furthermore, the portions of the total surface which are exposed to direct vertical fallout are isolated from one another so that electrical terminals at the ends of the bushing will not be short circuited by a column or path of ionized water. Furthermore, a bushing constructed according to our invention Will provide control of the path of such an ionized stream of water so that the water will fall through space rather than run across the complete creepage path between terminals.

Still further, our bushings are self-cleaning. This prolongs the period between necessary cleanings by servicemen, and permits more economical servicing.

In summary, in one embodiment we provide a bushing with a series of spaced major annular flanges or annular sheds, T-shaped in cross-section to provide a cylindrical rim portion, each of the sheds having an annular groove on the outside of the rim portion thereof which causes some of the deposited contamination when wet to Wash back to the bottom or root of this groove and around the periphery of the rim portion until it falls off. The undersides of the rim portions have sharp circular edges which will throw off such a wash, particularly when the bushing has a high voltage applied thereacross, and prevent establishment of an ionized path on the protected surface underneath the rim. In one embodiment we provide that approximately 46.5% of the total creepage path is protected from direct vertical fallout by the overhanging rim portions of the major sheds. Between each pair of major sheds there is an annular minor shed of considerably smaller diameter than, that of the major sheds, which prevents the formation of a conductive path on the bushing surface between the bases of the major sheds, by causing the wash off of the major rims to be carried around the periphery of the bushing and thrown off. A bushing constructed according to our invention is characterized by the absence of contaminant trapping pockets on the underside of the porcelain, and we can easily achieve a 2.83 creepage to strike-distance ratio between high voltage terminals.

In other embodiments of our invention we offer protection from vertical fallout to an even greater portion of the total creepage path, by providing spaced annular major sheds having rim portions disposed so that the sheds in cross-section are T-shaped or inverted L-shaped and the rim portions of which overhang a larger portion of the external surface of the shell or tubular portion of the bushing; or we provide spaced major sheds each of which includes mounted on and formed integrally with an annular disk portion a plurality of spaced concentric cylindrical rim portions of progressively increasing diameter and having a width several times that of the annular disk portion, so that the lower and upper surfaces of the rim portions, except the outer rim portion, are not exposed to direct vertical fallout.

Accordingly, a primary object of our invention is to provide a new and improved high voltage bushing suitable for horizontal mounting.

Another object is to provide a new and improved high voltage bushing in which the possibility of electrical flashover due to atmospheric contamination and moisture condensation is reduced.

Still a further object is to provide a new and improved high voltage bushing suitable for mounting in other than a vertical position and having a large creepage to strikedistance ratio.

These and other objects of our invention will become more clearly apparent after a study of the following specification when taken in connection with the accompanying drawings, in which:

FIGURE 1 is a cross-sectional view through a portion of a bushing according to the preferred embodiment of our invention;

FIG. 2 is a cross-sectional view through a portion of a bushing according to a second embodiment of the invention;

FIG. 3 is a cross-sectional view through a portion of a bushing according to a third embodiment of our invention; and

FIG. 4 is a cross-sectional view through a portion of a bushing according to a fourth embodiment of our invention.

Referring now to the drawings for a more detailed understanding of the invention, there is shown at 10 in FIG. 1 a high voltage bushing, which may be composed of porcelain, having a plurality of spaced major sheds generally designated 11 and a plurality of spaced minor sheds .12 between the major sheds, substantially equally spaced therefrom. The shell or tubular body portion 13 is seen to have 'a substantial portion of the entire surface thereof formed with the major and minor sheds. It is seen that each of the major sheds 11 has an annular groove 15 on the outside surface thereof, that each of the major sheds has a rim portion 16 with relatively sharp circular edges 17 and 18 on the under sides thereof, and that the thickness of the disk or stem portion 21 is relatively small compared to the width of the rim like cylindrical portion 16, so that the under edges of the rim portions 16 over-hang to a considerable distance the straight shed or stem portions 21.

While the bushing of FIG. 1 is mounted in a horizontal position, when the bushing is wet some of the deposited contamination is caused to wash back to the :root or bottom of the grooves 15 on the outsides of the major sheds 11 and around the periphery of the shed until the contamination falls off. This prevents all the contamination on the outer surfaces of rims 16 from washing over the edge and down the side of sheds 11 and onto the root or bottom portions 19. Furthermore, the sharp circular edges 17 and 18 on the under side of the shed rims 16 will throw off some of the wash from the outer surface of the rim, particularly when the high voltage is applied across the bushing, and prevent establishment of an ionized path on the underneath protected surface of the rim, the paths of the wash thrown off edges 17 and 18 being shown at 25 and 26. The minor sheds 12 prevent shorting out of the surface of the tubular portion of the bushing between the bases of the major sheds by causing the wash oti of the major sheds 11 to be carried around the periphery of the bushing and thrown oft.

Typical dimensions and operating characteristics of a porcelain bushing manufactured according to the invention would show that the curvature of portion 22 cor responds to the curvature of the arc of a inch radius circle; the distance between the centerline of the first or nearest major shed and the end v23 may be 1% inch; the height of the rim 16 may be /e of an inch; the groove may be A of an inch deep; the curvature of the .groove 15 may be that of the arc of a circle of A inch radius; the distance between adjacent sides of adjacent major shed rims may be 1% inches; the aforementioned sharp circular edges 17 and 18 may be curbed at a inch radius; the underneath curve or the where the rim joins the vertical shed portion 21 may be curved at a inch radius; the curve of the minor shed crests may be A inch radius; the distance between the centerline of a major shed and the centerline of an adjacent minor shed may be 1 inches; the diameter or the thickness of the stem or disk portion 21 may be inch; the minor sheds may be inch in height; the width of the rims 16 of the major sheds 11 may be 1 inches; the overall height of the major sheds may be 21 inches; and the distance between centerlines of adjacent major sheds may be 2 /8 inches. This provides for a bushing with an overall length of 29 inches from end 23 to the opposite end of the bushing, not shown, having ten major sheds, nine minor sheds, a total creepage distance of 86% inches nominal with a distance of 82 inches minimum, and a protected creep distance of 40 inches nominal. The creep distance to strike distance ratio is 2.83, and the ratio of protected creep distance to total creep distance is 0.465. The creep to line ground kilovolts equals approximately 1.7 inches per kilovolt when, for example, six of the bushings are used in series on a 500 kilovolt, three phase line.

Particular reference is made now to FIG. 2; the bushing generally designated 30 has spaced sheds31 each having an inner annular disk-like stem portion and an outer cylindrical rim portion extending parallel to the longitudinal axis of the bushing, the shed being generally T-shaped in cross-section with the rim portion 32 extending horizontally while the bushing is mounted in a horizontal position, each or the rim portions 32 having an annular groove -33 therein. By making the width of the rim portions 32 approach in value the value of the spacing between the centerlines of sheds 31, and making a the diameter of the annular disk portions quite large,

it will be seen that the ratio of protected creep distance to the total creep distance may be made very large, for example, considerably greater than 50%. In the example shown, the ratio of protected creep to total creep distance is approximately 50%. 'The grooves 3l3serve the same purpose as the grooves 15 in FIG. 1, that is, when the deposited contamination on any rim portion becomes wet' with fog or dew it washes back to the root of the groove 33 and around the periphery of the rim portion until it falls 01f.

Particular reference is made now to FIG. 3, where a bushing having an extended body portion generally designated 40 is seen to have spaced sheds generally designated 45, each shed including mounted on and formed integrally with an annular disk portion 41 a plurality of spaced concentric cylindrical rim portions 44 of progressively increasing diameter having a width several times that of the annular disk portion so that the lower and upper satisfies of all rim portions except outer rim portion 42 are not exposed to direct vertical fallout. Each of the outer rim portions 42 has an annular groove 43 therein. The bushing of FIG. 3 offers the maximum amount of surface which can'be protected from vertical fallout and the maximum ratio of protected creepage to total creepage distance. The bushing of FIG. 3 is particularly well adapted for heavily contaminated areas where fog or condensation frequently occurs but heavy rains are very infrequent or very unlikely.

The ratio of protected creep distance to total creep distance can be further increased by increasing the number of portions beyond that shown.

Particular reference is made now to FIG. 4 in which the bushing having an extended body portion generally designated '50 has spaced sheds 51 substantially inverted L-shaped in cross-section and having a rim portion 52 extending in a horizontal direction when the bushing is mounted horizontally. -I-t wll be seen that the ratio of protected creep surface to unprotected creep surface depends upon the width of the overhanging rim portion 52, the spacing between sheds 51, and the height of sheds 51.

If desired, a series of minor sheds may be placed between the series of major sheds 51 at spaced intervals, to serve the same purpose as the minor sheds 12 of FIG. 1.

The embodiment of FIG. 4 represents perhaps the embodiment which may be manufactured with greatest ease.

' The embodiment of FIG. 4 is effective at angles of from 45 degrees to 90 degrees with respect to vertical if the dog ears or rim portions 52 are pointing downward.

Minor sheds may also be added to the bushing of FIG. 3. i

, The term atmospheric fall out as employed herein includes smoke, dust and other mineral matter, and vegetable matter.

Whereas the bushings have been described as having shell or tubular portions, it will be understood that the bushings can be solid, if desired. The words body portion as employed in the claims appended hereto includes any tubular, hollow, or solid elongated portion of any suitable shape. Whereas round may be a convenient shape, wash oif from, for example, a decagonal shaped body portion'would also occur freely.

The annular grooves in the outer rim portions may be omitted if desired, where the self-cleaning feature provided by the grooves is not necessary.

The stated dimensions of the embodiment of FIG. 1 are exemplary and not limiting. Dimensions of the various embodiments may be varied to make a bushing fit available space, within limits which permit the advantages of the inventive features to be retained.

Whereas porcelain has been described as a suitable material for constructing the bushings of our invention, other suitable materials such as cast resin may be employed, including suitable epoxy resins.

Whereas we have shown and described our invention with respect to some embodiments thereof which give satisfactory results, it should be understood that the principles of the invention may be applied to other structures and modifications made without departing from the spirit and scope of the invention.

We claim as our invention:

1. As an article of manufacture, a high voltage bushing suitable for mounting in a horizontal position in a region of substantial atmospheric contamination and in a region of substantial moisture condensation, the bushing being composed of insulating material and having an elongated substantially cylindrical body portion, the body portion having a plurality of annular sheds at spaced intervals along the length thereof, each of the sheds including a disk portion extending from the body portion and having a cylindrical rim portion at the periphery thereof extending in both directions from the disk portion, each rim portion being spaced from the body portion of the bushing, the width of the rim portions, the

diameters of the disk portions, and the distance between sheds being chosen with respect to each other whereby at least one-half of the total creep distance is protected from vertical fallout while maintaining a sufiicient spacing between the edge of the rim portion of a shed and the adjacent edge of the rim portion of an adjacent shed to provide a safe strike distance for the voltage applied across the bushing while the surfaces of the rim portions are heavily covered with contaminating material.

2. A bushing according to claim 1 wherein the rim portions are additionally characterized as having annular grooves in the outer surfaces thereof, material Washing off the surfaces of the rim portions into the annular grooves and thence being carried to the underside of the bushing and discharged.

3. As an article of manufacture, a high voltage bushing for mounting in a substantially horizontal position, the bushing being composed of insulating material and having an elongated body portion having at spaced intervals along the length thereof a plurality of outwardly extending annular sheds, each of the sheds including a plurality of spaced concentric cylindrical rim portions of progressively increasing diameters mounted on and formed integrally with an annular disk portion extending from the body portion, the rim portions being substantially equal in width, the rim portions extending a substantial distance in both directions from the disk portion, the outer rim portion having an annular groove therein.

4. As an article of manufacture, a high voltage bushing composed of insulating material suitable for mounting in a position other than vertical, having an elongated body portion, having a plurality of sheds at spaced intervals along the length thereof, each of thesheds comprising a plurality of spaced concentric cylindrical rim portions of progressively increasing diameters mounted on and formed integrally with an annular disk portion extending from the body portion, the outer rim portion of each shed having an annular groove extending therearound, material washing into the groove and washing around the bushing to be discharged at the lower side thereof;

5. As an article of manufacture, a high voltage bushing suitable for mounting in a horizontal position in a region of substantial atmospheric contamination and in a region of substantial moisture condensation, the bushing being composed of insulating material and including an extended body portion having sheds at spaced intervals along the length thereof, each shed comprising at least two spaced concentric cylindrical 'rim portions of different diameters mounted on and formed integrally with an annular disk portion extending from the body portion, the rim portions extending in both directions from the disk portion, the underside of the outer rim portion and both the underside and upper side of other rim portions being protected from atmospheric fallout to thereby provide that the creep distance along the bushing surface which is protected from direct atmospheric fallout is a large portion of the total creep distance.

References Cited by the Examiner UNITED STATES PATENTS 1,166,394 12/1915 Steinberger 174-212 X 1,212,704 1/ 1917 Steinberger 174-212 1,304,247 5/1919 Barger 174-186 1,493,262 5/1924 Hammond 174-30 X 1,768,948 7/1930 Baum 174-212 X FOREIGN PATENTS 838,110 11/1938 France. 871,851 1/1942 France. 1,168,668 9/1958 France.

747,131 3/ 1956 Great Britain.

LARAMIE E. ASKIN, Primary Examiner. 

4. AS AN ARTICLE OF MANUFACTURE, A HIGH VOLTAGE BUSHING COMPOSED OF INSULATING MATERIAL SUITABLE FOR MOUNTING IN A POSITION OTHER THAN VERTICAL, HAVING AN ELONGATED BODY PORTION, HAVING A PLURALITY OF SHEDS AT SPACED INTERVALS ALONG THE LENGTH THEREOF, EACH OF THE SHEDS COMPRISING A PLURALITY OF SPACED CONCENTRIC CYLINDRICAL RIM PORTIONS OF PROGRESSIVELY INCREASING DIAMETERS MOUNTED ON AND FORMED INTEGRALLY WITH AN ANNULAR DISK PORTION EXTENDING FROM THE BODY PORTION, THE OUTER RIM PORTION OF EACH SHED HAVING AN ANNULAR GROOVE EXTENDING THEREAROUND, MATERIAL WASHING INTO THE GROOVE AND WASHING AROUND THE BUSHING TO BE DISCHARGED AT THE LOWER SIDE THEREOF. 